1. Field of the Invention
This invention relates to a transverse sealing mechanism for packed bags to be used when packing a product in bags of tubular resin film.
2. Description of the Prior Art
Conventionally used seal-cutting devices for cutting transverse seals of packed bags of tubular resin film include, for example, one which is disclosed in Japanese Utility Model Application No. 56(81)-54552 (Japanese Utility Model Laid-open No. 57(82)-167815) filed by the applicant of this invention. This device is shown in FIG. 4, and in the device 10 are disposed feed rollers 20, 20 for feeding tubular film 11, squeeze rolls 13, 13 synchronously rotating with and underneath the feed rollers 20, 20, heat-sealing means 14, 14 spaced apart, as required for heat-sealing, from and underneath the squeeze rolls 13, 13, and cutting means 15, 15 spaced apart at a distance about equal to the width of the sealed portion 16 from and underneath the heat-sealing means 14, 14. The squeeze rolls 13, 13, heat-sealing means 14, 14, and cutting means 15, 15 are provided respectively with displacing means 13a, 14a, and 15a, such as horizontally reciprocating cylinders. A timer means is provided (not shown) for operating the heat-sealing means after the squeeze rolls 13, 13 divide the content 12 in the film 11 and rotate while being closed to send the film 11 by a certain pitch. Further means are provided (not shown) for intermittently rotating the squeeze rolls 13, 13 to allow time for opening the heat sealing means 14, 14 after heat-sealing, sending downward the sealed portion 16 by a distance equal to the width thereof and cutting apart the portion thereafter.
The operation of packing and cutting by using this device will be described hereunder with reference to FIGS. 5(a), (b), (c) and (d).
FIG. 5(a) shows the condition wherein cutting of tubular film is completed after heat-sealing and the squeeze rolls 13, 13 are opened to fill the film 11 to its bottom with a charge (liquid).
FIG. 5(b) shows the condition wherein the squeeze rolls 13, 13 are closed together to divide and pack in the bag 11a the charge 12 of an amount for one pack. Then, the heat-sealing means 14, 14 and seal-cutting means 15, 15 are in the opened condition.
FIG. 5(c) shows the condition wherein the squeeze rolls 13, 13 rotate while being closed, the tubular film 11 descends in closely collapsed condition, the charged bag 11a is stopped after passing the heat-sealing means 14, 14 to the underside thereof, and the collapsed portion 11 of the tubular film is heat-sealed by closing the heat-sealing means 14, 14.
FIG. 5(d) shows the condition wherein the heat-sealing means 14, 14 are opened after heat-sealing, the squeeze rolls 13, 13 intermittently rotate by a circumferential length Wb to send the film 11 downward by an amount Wa and stop thereafter, the cutting means 15, 15 then being closed to cut the sealed portion 16.
In this transverse cutting means 15, 15 of the prior art, as shown in a larger scale in FIG. 6, a projecting cutting blade 15b is formed on one side and a recessed section 15C is formed on the other side, the heat-sealed portion 16 of the film 11 being cut immediately after heat-sealing by the cutting blade 15b and section 15C, and at the same time the portion 16 being held therebetween and compressed by means of the pressing cylinders 15a, 15a.
In this transverse cutting means 15, 15 of the prior art, cutting operation has already started before the sealed portion 16 of the film 11 is held between and compressed by the abutting faces 15P, 15P, and the means 15 for cutting after compression does not have any cooling means so that cooling of the sealed portion is not necessarily complete. Therefore it occasionally happens that the sealed portion is not strong enough.
Further, even though cooling can be provided to the cutting means 15, 15, compression through means such as cylinders is not sufficient, and also in the case of a structure such as cams, this mechanism functions to apply a constant pressure so that the cutting means may not be able to accommodate various compressing conditions due to the thicknesses and variety of materials of film 11. Therefore the sealed portion sometimes does exhibit sufficient strength.
Furthermore in the cutting means of the prior art, the cutting operation is initiated in advance so that seal strength is not necessarily improved by compression. The method for cutting after compression also does not permit cooling to be performed completely, and the mechanism for compression cannot accommodate a variety of film materials.